Study Of Tissues And Diversity In Shapes And Sizes Of Plant And Animal Cells

Aim Of The Experiment

To study the different tissues and diversity in sizes and shapes of animal and plant cells such as guard cells, palisade cells, parenchyma, sclerenchyma, collenchyma, phloem, xylem, squamous epithelium, mammalian blood smear and muscle fibres through the preparation of permanent/temporary slides.

Theory

What is tissue?

A tissue is a cluster of cells that perform a shared function that are similar in size and shape. Tissues can be grouped as follows:

  • Simple tissue – They contain one type of cells only. Furthermore, they can be classified into:
  • Parenchyma
  • Collenchyma
  • Schlerenchyma
  • Complex tissue – They possess more than one cell type
  • Meristematic tissue
  • Permanent tissue

Cells of various types of tissues vary in their size, structure, shape, wall composition and function.

Related Link: The Plant Tissue System

Requirements

A. Permanent Slides of:

  • T.S of Nerium Leaf, T.S of Lotus leaf, T.S of Lotus stem/petiole
  • V.S of root apex and shoot apex
  • T.S of Mentha/Cucurbita stem
  • Macerated material of Tridax, Vitis/Bougainvillea

B. Requirements for Maceration Technique

  • Tiny twigs of locally accessible plants
  • Safranin
  • Glycerine
  • Beaker(100ml)/Boiling test tube
  • Cotton blue
  • Slides
  • Glass rod
  • Needles
  • Tripod stand
  • Burner
  • Wire gauge
  • Microscope
  • Knife (sharp-edged)
  • Thread
  • Cheese/muslin cloth

Maceration Fluid

  • Chromic acid should be dissolved with an equal quantity of 10% nitric acid
  • Preparation of chromic acid is done by adding 100ml of concentrated H2SO4 gradually in 10ml of water
  • Now add K2Cr2O7 (potassium dichromate) – 50gm
  • The stock solution is ready. 10ml of this solution is diluted up till 100ml for the preparation of the working solution of the maceration liquid.

Procedure

  • Pick some fine green younger branches from a locally accessible woody plant. Thickness – that of a toothpick.
  • Snip the twigs into smaller bits of 0.5cm long
  • Shift the pieces to beaker holding water. Boil it for 10-15minutes until the sample settles at the base
  • This way the air inside the sample is removed
  • Shift the material into a beaker holding the maceration fluid. Bring it to a boil until it turns pulpy and soft for close to 10-15 minutes.
  • The muslin cloths to the beaker’s mouth. With tap water, rinse the material continuously in order to eliminate the traces from the maceration fluid.
  • Add some drops of safranin to the material in order to stain the xylem or for phloem – cotton blue
  • Onto a glass slide, place the stained material in a drop of glycerine.
  • Split the cells using two needles
  • Plant a coverslip onto the slide and observe under a microscope
  • Sketch your observation. Compare with the diagram given

Analyze the following slides:

  • For spongy and palisade tissue – T.S of Nerium Leaf
  • For Aerenchyma – T.S of Lotus petiole. Lotus leaf
  • For meristem – V.S of root and shoot apex
  • For simple tissues – T.S of Mentha stem or Cucurbita

Observations

  • Chlorenchyma is parenchyma cells comprising of chloroplasts. They may have spongy or loosely arranged cells or palisade – columnar cells compactly aligned.
  • It is aerenchyma if there is a presence of large intercellular spaces into the cells.
  • The protective tissue or the epidermis is the parenchyma tissue forming the outer covering of leaves, stem or root.

Differences between different types of simple tissues:

Properties

Parenchyma

Schlerenchyma

Collenchyma

Cell wall

Thin, presence of primary wall only

Thick

At the corners, thick primary wall

Cell arrangement

Arranged loosely

Compactly arranged

Compactly arranged

Nature of cells

Living. Presence of nucleus

Cells are dead. Absence of cellular contents

Living. Nucleus observed

Shape

Oval, polygonal, spherical, rod-shaped or rectangular

Elongated

Variable shape

Intercellular Space

Many

Absent

Absent

Vacuoles

Vacuolated cells

Absent

Absent

  • Section of the leaf need to be observed
  • Mesophyll of the leaf is covered by lower and upper epidermis
  • Lower epidermis exhibits small pores known as stomata. In some plants, both the lower and upper epidermis of the leaf show stomata.
  • Tissues are observed for their characteristics, position in the different parts of the material of the plant.
  • Sketch diagrams to display the tissue type and their locations.

Viva Questions

Q.1. Why does aerenchyma have large air spaces?

A.1. It is because they promote gas circulation through large air spaces and render buoyancy.

Q.2. Name a plant type where aerenchyma cells are found.

A.2. In aquatic plants. Example: Hydrilla.

Q.3. Write about the constituency of the sclerenchyma cell wall.

A.3. They have thick cell walls containing lignin with high levels of cellulose content.

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